HYDROCARBYL DERIVATIVES OF UCL2HB(PZ)32 : SYNTHESIS, CHARACTERIZATION AND REACTIVITY STUDIES TOWARDS PROTIC SUBSTRATES AND KETONES

Abstract The reaction of [UCl 2 HB(pz) 3 2 ] ( 1 ) with lithium alkyls LiR (R = Me, CH 2 SiMe 3 , C 6 H 4 - o -CH 2 NMe 2 ) in the 1:1 or 1:2 molar ratio affords the compounds [UCIRHB(pz) 3 2 ] (pz = C 3 H 3 N 2 , R = Me ( 2 ), CH 2 SiMe 3 ( 3 ), C 6 H 4 - o -CH 2 NMe 2 ( 4 )) and [UR 2 HB(pz) 3 2 ] (R = Me ( 5 ), CH 2 SiMe 3 ( 6 )) respectively in 60–80% yield. Complex 2 can also be obtained (60% yield) by redistribution at room temperature between the complexes 1 and 5 . Compounds 2, 3 and 4 react with pzH providing [UCl(pz)HB(pz) 3 2 ] ( 7 ) in almost quantitative yield and 5 and 6 react also with pzH leading to [U(pz) 2 HB(pz) 3 2 ] ( 8 ). The alkoxide [U(OC 6 H 4 - o -OMe) 2 HB(pz) 3 2 ] ( 9 ) was synthesized by reacting 5 or 6 with guaiacol. By reacting the chlorohydrocarbyls 2, 3 or 4 with excess of acetone the aldolate [UCl(OCMe 2 CH 2 (C=O)Me)HB(pz) 3 2 ] ( 11 ) was obtained, due to the activation of α -CH bond of acetone; however, for 3 the reaction is not clean and a mixture of 11 and [UCl(OCMe 2 CH 2 SiMe 3 )HB(pz) 3 2 ] ( 12 ) is always obtained. Stoichiometric amounts of acetone insert into the metal-carbon bonds of 2 and 5 yielding [UCl(O t Bu)HB(pz) 3 2 ] and [U(O t Bu) 2 HB(pz) 3 2 ] respectively, while the insertion product [U(OCMe 2 CH 2 SiMe 3 ) 2 HB(pz) 3 2 ] ( 10 ) can only be obtained when 6 reacts with excess of this substrate. 9 crystallizes from toluene/hexane in the triclinic space group P 1¯ with unit cell dimensions a = 12.295(2) A, b = 12.640(2) A, c = 13.994(2) A, α = 76.10(1)°, β = 72.50(1)°, γ = 80.71(1)°, V = 2004(2) A 3 and Z = 2. Recrystallization of a mixture containing [UCl(O t Bu)HB(pz) 32 ] and 11 led to a decomposition product which has been characterized by X-ray structural analysis as [UCl(Hpz)(O t Bu)(μ-O)B(μ-pz)(pz) 2 ] 2 ( 13 ): monoclinic P 2 1 / n , a = 13.701(3) A, b = 11.337(2) A, c = 14.857(4) A, β = 104.65(2)°, V = 2233(1) A 3 and Z = 2. Extended Huckel molecular orbital calculations provided some information on the bonding capabilities of the [UHB(pz) 3 2 ] fragment compared to [U(C 5 Me 5 ) 2 ] and on the vulnerability of the poly(pyrazolyl)borate ligands to nucleophilic attack.